The results of the third phase of Pisa (Programme for International Student Assessment) make interesting reading. Every three years, Pisa tests 400,000 15-year-olds from 54 countries in reading, maths and science. Like all international assessments, Pisa has methodological and statistical limitations. The Organisation for Economic Cooperation and Development (OECD), however, uses elaborate procedures to ensure that the sampling of students and schools is fair and that like is being compared with like. The tests are not related to any specific curricula but are based on the knowledge and skills young people need in the modern world.

The Pisa results provide lots of information about the efficacy of national education systems. How good they are, however, also depends on what happens to the young people after 15. Some countries, such as Norway and Denmark, perform only at average or below in Pisa but, aided by good upper-secondary schooling, still produce well-educated young adults.

The UK has participated in all three phases of Pisa. In 2000, British performance - seventh place in reading, eightth in maths and fourth in science - was welcomed by Tony Blair. The 2003 results were hardly discussed because the UK sample was too small for the OECD to be certain that it was truly representative, and the results were omitted from the published report. Subsequent statistical analyses, however, revealed that the sample was slightly better than "representative". The results, which showed a decline on 2000, might have been worse had the sample been normal.

The latest stage has received remarkably little press coverage, and yet it confirms the decline from 2000. In reading, the UK average score dropped from 523 in 2000 to 495 - only just above the OECD average. In maths, the fall is from 529 to 495 - below the OECD average. In science, the slippage is less marked - from 532 to 515, still well above the OECD average.

The wide confidence intervals of the scores do not allow any certainty but they suggest a downward trend over the past seven years. Furthermore, the UK results show relatively large gaps between the scores for the 95th percentile (highest scoring) and the fifth percentile (lowest scoring) groups except in maths. In contrast, Finland not only achieves high average scores (the highest in maths and science and second only to Korea in reading) but also has some of the smallest spreads of scores. Its education system is both high achieving and highly equitable.

Canada, Hong Kong and New Zealand perform well in reading. In maths and/or science, they are joined by Australia, Switzerland, Netherlands, Ireland, Liechtenstein, Taiwan, Macao and Japan. All the scores for France are below the OECD averages, have large spreads and are tending to decline. Germany and Sweden do a little better. Poland is at the average and is improving. Denmark does well only in maths. US students do not do well.

The suggested decline of the UK scores - in contrast to the rising trends of national Sats and GCSEs - raises questions about the direction of educational policy in England over the past 10 years. Have teachers been conditioned into "teaching to our tests" rather than promoting pupils' broader knowledge and skills? (The separate results for Scotland, Wales and Northern Ireland need to be considered in relation to their increasingly different systems).

Is it time to question whether a test-dominated, market-based system - which now includes a proposal from Lord Adonis that league tables show proportions of high achieving pupils - is the best way to achieve world-class education?

Perhaps the government should consider some more radical ideas, influenced by the Finnish system, proposed by the National Union of Teachers in its pamphlet A Good Local School for Every Child and for Every Community. If we aspire to Finland's excellent results, it would be a good idea to reflect on how they have been achieved.